You don’t want to eat tofu and rabbit food so you can live long enough to develop dementia? Quitter.
I want to live a healthy lifestyle not primarily to live longer (other than the not smoking the gain in life expectancy is modest) but in order to live pretty much those same years without dementia or other disability. Living more years is not the main point; living the years I live better is.
Not really comparable figures. The second one is a result similar in many different studies. Moreover medical science can to a significant degree say how smoking causes ailments which shorten life.
With diet (vegetarian or other) it’s much more of a morass of differing results from different studies and trying to separate correlation from causation.
Here’s just one example, account of a recent re-study of ‘the Mediterranean Diet’, albeit not vegetarian but long held as being ‘shown’ to have significant health benefits. A recent study, in Italy, found it did for high income/education groups, but showed no benefit for lower income/education people who followed it, with only quasi-speculative explanation why (quality of food).
There’s all kind of social factors in the effect of diet, which is itself hard to define (as in the issue raised in the study above exactly which diet, if that’s even really the reason for the difference). It’s just much harder to study as a stand alone causal factor than smoking.
Again, something like a person being far overweight might be a reasonable factor to compare to whether they are a smoker in effect on life expectancy. Some superficial description like ‘eats meat’ or even ‘goes to McDonald’s often’ (how much is often? and orders what?, etc) just doesn’t tell you very much that science can accurately map to life expectancy.
Nonetheless, my impression is that diet alone has an impact on life expectancy of less than 5 years, while smoking is closer to 10 years. So smoking is the bigger risk factor than diet or exercise.
On the subject of the Mediterranean diet, I saw this study once. It compared a control group, Mediterranean diet with olive oil, Mediterranean diet with peanuts.
http://www.nejm.org/doi/full/10.1056/NEJMoa1200303
It appears the gap between the control group and the olive oil group was as big as the olive oil group and the nut group.
Which begs the question, can’t you just eat the nuts and not totally revamp your diet?